I am hoping someone can help me.
I have a time variable coded as months from Jan 2016 to Feb 2020
I am hoping to fit some splines to my regression model to analyse trends over time
For this I need two variables, one is "before" and one is "after", which reflect time before and after the implementation of a policy
I need "before" to run as 0, 1, 2,3,4 etc upto March 2019, and "after" to run 0,1,2,3,4,5 from April 2019
Does anyone know some quick code which can help with this?

Thank you